Monday, April 20, 2009

Game theory and Cooperation in Social Systems

It's almost 2am, but I have been thinking about a summary of a recent Nature paper I read while I was in Boston visiting MIT. I had picked up the article in MIT Tech Talk on a whim during a visit to the Stata Center where MIT's CSAIL laboratory is located.

This article helped me start thinking about the conundrum of:
- why there are so many people willing to spent so much time shuffling and passing links to other people?
- why people write Wikipedia articles when they can spend time doing other things?
- why do users tag photos and URLs when the majority of the benefit is for others to find these items more easily?
In short, why is it that entities in social systems cooperate, especially when the benefit to oneself is not entirely clear at all?

Turns out researchers of microbes have been thinking about some of these cooperation problems as well. "One of the perplexing questions raised by evolutionary theory is how cooperative behavior, which benefits other members of a species at a cost to the individual, came to exist." They have used yeast as a model for understanding what might be happening. Sucrose is not yeast's preferred food source, but some yeast cells will metabolize it when glucose is not available, but the sugar diffuse away, and other free-rider yeast cells (lazy bums!) then benefits from the sugar for free.

Well, if the sugar diffuse away completely, then there is no reason to be the 'cooperating' cell to spent all that energy to benefit others. It gets really interesting when the cooperating yeast cell have preferential access to, say, 1 percent of the sucrose they metabolize. This slight advantage not only allow for the cooperating cells to compete effectively against the cheaters, but also enable the entire yeast community to benefit from having sucrose as an alternative food source. Moreover, no matter what the starting numbers of yeast cells, they end up into an equilibrium state with just the right amount of cooperating cells and cheaters present after some evolutionary period. The MIT team used game theory to model this entire process, and showed why it works the way it does. Darn cool!

This got me thinking about agents in a social system sometimes behave in similar ways, and can be modeled using game theory. I'm sure some of this has already been done. This sort of study is common in behavioral economics, for example. But how does it apply direct in social web system modeling? How can it help explain, for example, the tagging behavior of users in flickr? Perhaps the little bit of benefit that the user gains from organizing photos that she owns or have found is enough to turn them into 'cooperating' agents, from whom other freeriders obtain benefit. Moreover, the idea could be used to model why there are just the right pareto-balance (and power-law distributed) of cooperating agents and freeriders in a social web system.


Jeff Gore, Hyun Youk & Alexander van Oudenaarden.
Snowdrift game dynamics and facultative cheating in yeast.
Nature advance online publication 6 April 2009 | doi:10.1038/nature07921


Brendan said...

This area is really underexplored. Except in online auctions, of course. Microeconomic models always need a good deal of adjustment to handle real-world data though.

Ed H. Chi said...


The interesting thing about models is that they sometimes offer insight into the problem we're interested in studying. In this case, you're right that we have been paying attention to micro-economic models to see if they apply.

What's perhaps interesting is that much of this kind of data was hard to obtain for social scientists to study, but now it is all possible, thanks to Social Web sites.

Utopiah said...

Very interesting indeed, I guess it's always the perceived advantage, an expected return on investment that always drives the process. Free riders probably either have a more encompassing model or are not looking for the same set of return.

On this topic I think those papers could be interesting too :

How do selfish agents learn to cooperate?, Akira Ito, Artificial Life V: Proceedings of the Fifth International Workshop on the Synthesis and Simulation of Living Systems, MIT Press, pp. 185-192, 1997,M1

Emergence of Adaptive Society with Competitive Selfish Agents, Takashi Ishida, Hiroshi Yokoi and Yukinori Kakazu, 1999

Cooperative Multi-Agent Learning, Liviu Panait and Sean Luke, Department of Computer Science, George Mason University, 2005

Ed H. Chi said...

thanks for those pointers, Utopiah. I'll take a look at them for sure.

There is a whole set of agent simulation work that is aimed at modeling complex social systems. It's an area of research that I have been meaning to read more about.

Mariana Soffer said...

In the 1960s, Jacques Derrida described a trace as the “mark of the absence of a presence” – which is precisely what happens to our digital “selves”. We are socially connected, operate in a sense-and-respond mode, exercise social judgement and all the while, leave our presence in places where “we” no longer exist. For all intents and purposes, the social web is Deconstruction made manifest.

So probably people colaborate with each other to show that they can perpetuate themselvez through their actions.

I do not agree with this conclusion, first because it is a blunt generalization and second because I am not sure that the assertions where the idea is based on are true. I wouldn't no how to explain why people do these things.

Ed H. Chi said...

When folks start to talk about intrinsic vs. extrinsic motivations, it can get pretty psychological and philosophical very quickly indeed.

There are a wide variety of possible reasons why people participate in social networks, including (1) the fact that we're inherently social animals (that's why we have solitary confinement as a punishment); (2) need for social stature and power; (3) to leave a mark in the world (as you said); (4) possible advantages in acquiring further wealth based on reputation; (5) fame; (6) sex. I think for different social networks people participate for different reasons. Facebook, started as a social dating site, for instance, but now it has become a place for people to communication and to gain reputation in your friendship circle.

It's a complex topic, that's for sure.

Mariana Soffer said...

Txs for sharing your thought.
regarding to point 1 there is this saying: “What differentiates humans from all other creatures is the deep and unquenching desire to be appreciated.” , which affirms what you say.
I completely agree about with you say, I just want to understand more. I will keep thinking

Ed H. Chi said...


It may be worth pointing out that the game theoretical approach for explaining behavior is not limited to the cost and benefit in terms of food or money or some other tangible measurements. It can be applied, even if the advantage is intangible, such as reputation or position within a social network. What I'm trying to say is that what the research points out fundamentally is that as long as there is some net benefit to the agent, a system can elicit cooperative behavior.

Mariana Soffer said...

Now I perfectly understand you, thanks a lot for clarifying

Rizwan Tayabali said...

Slightly tangentially and moving away from web systems, I recently wrote a post on whether game theory and cooperation for social organisations @ - thought you might find it interesting.